1. Field of the Invention
This invention relates to delimiters and particularly to retractable delimiters.
2. Description of the Prior Art
Rural airports do not generally have the types of facilities used at major airports. For example, many of these airports do not have runway lighting. The runways are marked by delimiters—cones that are placed at regular intervals along the sides of the runway. These cones are visible to pilots and enable them to see the edges of the runway. When the runway needs maintenance, e.g., when snow must be removed, the delimiters become obstacles to the cleaning process. Thus, a crew must physically remove the cones before the runway can be plowed. This may mean having a worker walk the length of the runway to move the cones. Once the snow is cleared, the cones have to be replaced. This also requires time and labor to perform.
To eliminate the need to remove cones or other delimiters, several retractable types of delimiters have been invented. These delimiters can be retracted into the ground when they are not needed and then raised when they are needed. Many of the patents for these types of delimiters are directed to highway and parking lot use. For example, large arena parking lots often need to set cones for traffic flow into the parking lot. Use of the retractable delimiters allows the parking crew to raise those units as needed to create the proper traffic flow. As time progresses and the traffic flow must be adjusted, delimiters can be raised and lowered as needed
Examples of these devices are found in the following U.S. Pat. Nos. 364,175, 3,086,430, 5,425,595 and 5,819,471.
One problem with all of these designs is that they are unsuitable for use at airports. Under aviation rules, any delimiter must collapse when struck be a wing. A freestanding cone presents no danger to an airplane. However, a rigidly installed retractable delimiter does present such a danger. These devices are not designed to flex or break when hit and can therefore cause serious damage to an airplane.